Yeah so that's one person... what about the others nearby being convicted because they wore black?

Clearly because they all wore black, they all planned on shooting an officer. /s

With this logic the police could just have someone go into a group of peaceful protestors with matching clothing, and then shoot at an officer to justify the entire protest being classified as terrorism.

There's a reason that's not the way this is designed to fucking work. And it's the exact reason non-dumbasses have been saying the terrorism laws have been overly broad since the beginning. They're a blank check for authoritarianism and fascism.